1. Field of Invention
The present invention relates to a gray-scale method. More particularly, the present invention relates to a gray-scale method for a flat panel display.
2. Description of Related Art
The traditional gray-scale methods used for a flat panel display include area ratio gray-scale (ARG) and time ratio gray-scale (TRG). The principle of the area ratio gray-scale is to generate different human visual perceptions regarding brightness by the use of a plurality of combinations of usage area. If it is intended to generate a N-bit gray-scale effect, 2N pixels are needed in the intended area. The human visual perception for the gray-scale effect is generated by the use of the ratio of the bright pixels and the dark pixels in the 2N pixels. FIG. 1 is a pixel diagram for generating a plurality of 2-bit gray-scale pixels by the use of area ratio gray-scale. The methods for combining the pixels 110˜140 represent a collection of four different gray-scale combinations 150, respectively, in which each gray-scale combination includes four sub-pixels. Regarding the first area ratio pixel combination 110, it includes four fully turned-on (fully-lit) sub-pixels 112˜118, and the gray-scale level for which is the brightest as shown by the gray-scale effect 115. The second pixel combination 120 includes a turned-off (dark) sub-pixel, which the result is as shown by the gray-scale effect 125 by which the color is obviously deeper than the gray-scale effect 115. The gray-scale effect 135 is formed by the third pixel combination 130 in which the ratio of the on and off pixels is 1 to 1, and the color of the gray-scale effect 135 is deeper than the color of the gray-scale effect 125. The gray-scale effect 145 is formed by the fourth pixel combination 140, and of which has the darkest color. Because the area ratio gray-scale requires 2N pixels for forming the N-bit gray scale, its resolution is greatly decreased and its gray-scale effect is not able to be easily improved to a higher-bit gray scale effect. Therefore, it is not a gray-scale method suitable for a high-performance display.
Another time ratio gray-scale is intended for achieving the N-bit gray-scale effect by dividing a frame period into 2N sub-frame periods. Since human visual perception has a sensory integration effect, the eyes are able to feel the gray-scale effect as long as the on/off times of the pixels are controlled during a frame period. FIG. 2 is a pixel diagram of a 2-bit time ratio gray-scale displaying method. The sub-frame periods F1˜F4 are combined to form a complete frame period F. By controlling the on/off of the pixels during an individual sub-frame period, the pixels are able to achieve the gray-scale effect during a complete frame period F. The first time ratio gray-scale combination 210 is fully-on (fully-lit) to form the gray-scale effect 215, while three time ratio gray-scale combinations 220˜240 form the gray-scale effects 225˜245, respectively. The luminosity intensity differences between the fully-lit and dark gray-scale effects are evident from FIG. 2. FIG. 3 is a timing diagram of a plurality of sub-frame period of the time ratio gray-scale. A gate driver generates a first initial pulse 310 at a first scan line G1. The first initial pulse 310 occupies a horizontal period. Then, a gate pulse is transmitted to the next scan line G2, G3 . . . GN sequentially via a shift register during each horizontal period. The first initial pulse 310 enables the pixels on the display panel sequentially. A source driver is used for outputting the required display data D1˜DN to the pixels on each scan line. By controlling the first initial pulse 310 within each sub-frame period during the timing 300, the combinations of the sub-frames F1˜F4 as shown in FIG. 2 can be achieved and the desired gray-scale frame combination is formed. However, the time length of the sub-frame period in the time ratio gray-scale must be ½N times of that of a complete frame period. In other words, it is required to increase the working frequency of the peripheral circuits of a display by 2N times. Therefore, the circuit complexity, power consumption rate, and the heat dissipation problems are increased significantly.
Most of the current liquid crystal displays adopt the above two gray-scale methods, or a combination of the two above methods for achieving a higher resolution. However, the decrease of the resolution and the increase of the working frequency for the circuit still cannot be solved at the same time.